Brakes: 1977 Rear calipers

[Bob 1967]

Hi all, I'm new to the forum.
Just recently I purchased a Jubileum 1977 244.
I have had bikes previously and a 72 280CE and a 90 200TE .
First thing I normally do after purchasing any car is Tyres and brakes.
I put new Uniroyal tyres all round. I took it out 3 times for short runs about 5 miles.
On Tuesday I was pulling up to a red light at a crossroads ,it was a 50kph zone(30 mph approx.)and I had lifted off(automatic ). at about 100 yards I began to apply the brakes (foot went to the floor!)-nothing tried again ,several times pumping - nothing (red light came up "Brake Failure") tried hand brake as last resort-nothing.
I narrowly avoided T boning a car ,I aimed behind him and missed.
I do acknowledge it is my own fault, buyer beware etc. But....
I got the car home and horrors unfolded.
Both rear calipers had had their bleed screws removed and bolts screwed in their place ,they were in effect useless the seals were perished. and pistons seized.
I've already bought a new master cylinder ATE. I plan to do the whole system including all lines.
I am at the moment searching for replacement rear calipers, the originals were Girling (two piston), what I need to know is, are other calipers compatible ?
Lucas etc. and are calipers year specific or will later 240 model calipers fit?

Sorry it was a bit long winded, but it was the most freighting experience I have had while driving.
Bob.